Temperatures reach over 100 degrees on the Plateau Record temperatures hit area as heat wave passes through Western Washington July 29, 2009 7:01 pm Tags: Bonney Lake-Sumner Courier-Herald The Mt. Rainier Bank sign in Buckley shows that temperatures on the Plateau reach 102 degrees July 29 – the hottest day of the year. Tags: Bonney Lake-Sumner Courier-Herald